1. Field of the Invention
The present invention relates to an attachment structure of a lens unit, and more particularly to an attachment structure of a CCTV lens unit for attaching the lens unit to a CCTV camera.
2. Description of Related Art
In a closed-circuit television (CCTV) lens unit of a CCTV camera, a taking lens is mounted in a casing of the lens unit, and the casing is provided with an attachment ring for attaching the lens unit to a camera body by engaging in the camera body. The lens unit includes an iris unit comprising an iris and an iris meter. The iris unit is supplied with electricity from the camera body via a cable of the iris meter connecting with a connector of the camera body.
The casing and the attachment ring of the lens unit connect via projections. When the casing is rotated in a fastening direction to attach the lens unit to the camera body, the rotational force of the casing is transmitted to the attachment ring through the projections, so that the attachment ring is rotated and engaged to the camera body. After fastening the attachment ring, the casing is rotated in an opposite direction (i.e. a loosening direction) within a rotational angle limit so as to adjust the position of the cable to easily connect with the connector. If the casing is rotated in the loosening direction more than the rotational angle limit, the projections come in contact with one another and the attachment ring is rotated and loosened.
In the conventional lens unit, contact faces of the projections of the casing and the attachment ring are parallel with the radial direction of the attachment ring, and stress may concentrate at base corners of the projections as a result. Thus, if an excessive rotational force is transmitted from the casing to the attachment ring, that is, if the attachment ring is over-fastened after fastening the attachment ring, there is a disadvantage in that the projections are broken. Such a disadvantage can be overcome by strengthening the projections by enlarging them; however, if the projections are enlarged, the rotational range of the casing to adjust the position of the cable is seriously narrowed.